Template bugfix and cleanup

Pulled "getFilledTemplate" out of __toString(), ensure that __toString()
never throws an exception.
Added some docstrings.
Update README
Removed some unused functions from sql.php

Removed sql_get_all()
Removed sql_remove_where()
Removed reference to sql_remove_where() from Addon delete()
Fix DEBUG_MODE constant use
Merge pull request #7 from stephenjust/master

Fix template bug, doc changes to help GSoC students get started, remove some unused sql code
Fix 'Use of undefined constant TMP - assumed 'TMP' in stkaddons/include/Template.class.php line 21'
Remove dependency on sql_exist()
Remove dependency on sql_update();
Remove dependency on sql_insert()
Fix typo in Addon::setName
Merge pull request #12 from leyyin/master

Fix TMP issue and remove old sql dependency